THE LIVER AND BILE 761 



During its stay in the bladder the bile is concentrated by the loss of 

 water and by the addition to it of nmcin or nucleo-albumen, derived from 

 the cells lining the bladder. Of the other constituents of bile, the pigments 

 must be regarded simply as waste products, and an index to the disintegra- 

 tion of haemoglobin. Their mode of origin will be discussed in dealing with 

 the history of the red blood corpuscles. They pass into the intestine and 

 are there converted by the processes of bacterial reduction into stercobilin, 

 which is excreted for the most part with the faeces, a small proportion being 

 absorbed into the blood vessels and turned out in a more or less altered 

 condition as the pigments of the urine. From the point of view of digestion, 

 the important constituents of bile are the bile salts, with the lecithin and 

 cholesterin held in solution by these salts. The time relations of the secre- 

 tion, as well as of the flow of bile into the intestine in connection with the 

 processes of digestion, can be learnt from animals in which the bile is 

 conducted to the outside of the body by means of a permanent fistula. 



For this purpose Pawlow has devised the following operation : In the dog the 

 abdomen is opened, and the common bile duct sought as it passes through the intestinal 

 wall. The orifice of the duct, with a piece of the surrounding mucous membrane, 

 is cut out of the wall of the intestine, and the aperture thus made sutured. The 

 excised portion of mucous membrane, with the opening of the duct, is then sewn on to 

 the surface of the duodenum, and the loop of duodenum at this point is stitched into 

 the abdominal wound. After healing, the natural orifice of the bile duct is thus made 

 to open on the surface of the abdomen. 



In an animal treated in this way the flow of bile from the fistula is found 

 to run parallel to the pancreatic secretion. Although smaller in amount, it 

 rises and falls with the latter. Thus a meal of meat produces a large flow of 

 bile, a meal of carbohydrates only a small flow. Moreover, beginning almost 

 immediately after taking food, it attains its maximum with the pancreatic 

 juice in the third hour and then rapidly declines. 



In the production of this flow of bile two factors may be involved : (1) the 

 emptying of the gall bladder; (2) an increased secretion of the bile. In 

 order to determine the relative importance to be ascribed to each factor, 

 we must compare the results obtained on an animal possessing a Pawlow 

 fistula with those obtained on an animal provided with a fistulous opening 

 into the gall bladder, the common bile duct in the latter having been ligatured 

 to ensure that the total secretion of bile passes out by the fistula. In such 

 animals we find, as we should expect, that the secretion of bile is a con- 

 tinuous process, but that, synchronously with the great outpouring of bile 

 into the intestine during the third hour after a meal, there is an increased 

 secretion of this fluid. The passage therefore of the semi-digested food 

 from the stomach into the duodenum causes not only a slow contraction 

 and emptying of the gall bladder but also an increased secretion of bile by 

 the liver. What is the mechanism involved in the production of these two 

 effects ? The muscular wall of the gall bladder, as has been shown by Dale, 

 is under the control of nerves derived both from the vagus and from the 

 sympathetic, the former conveying motor and the latter inhibitory impulses. 

 It is usual to suppose that the entry of acid chyme into the duodenum 



